1. Field of the Invention
The present invention relates generally to heating, ventilating, and air conditioning (HVAC) and more particularly to an apparatus and method for increasing entrainment, mixing and spreading of air directed into a room or other enclosure.
2. Description of the State of the Art
Heating, ventilation, and air conditioning (HVAC) systems are installed in modern buildings to enhance comfort. Those systems not only provide warm or cool air, as needed to maintain room temperature within desired ranges, but also supply fresh air to dilute and replace ambient room air that becomes depleted of oxygen due to human consumption, and that becomes polluted by human habitation and other sources, such as chemical release from carpets, paint, copy machines, and the like. Current standards of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) set in 1989 require a minimum fresh air ventilation rate of 7.1 liters/second/person (15 cfm/person) for general buildings and 9.4 liters/second/person (20 cfm/person) for office buildings.
Adequate exhausting of pollutants from a room or building is necessary and is accomplished by diluting the pollutants inside with fresh air from outside, while drawing some air out of the room through a return duct. To do so efficiently, the fresh air from outside must be properly distributed in the room to prevent a short circuit of the incoming air flowing directly to the return duct. Such short circuited air streams that flow directly from the fresh air inlet to the outlet or return duct without mixing adequately with the other air in the room cause stagnant air zones, relative discomfort, and inefficient use of energy. Consequently, it is necessary to achieve effective mixing of the incoming air with the ambient air to achieve good ventilation, exhaustion of pollutants, and effective distribution of heated or cooled air.
Introducing or injecting air into a room through a narrow, elongated nozzle or duct outlet to produce a substantially planar (narrow, elongated) jet of air into the room has been found to be a reasonably effective way to achieve mixing of the incoming air with the ambient air in a room by the process of air entrainment. Entrainment is a process of vortex generation, engulfment of ambient fluid, and turbulent transport and includes the dissipation of turbulent energy and momentum transfer from the interior of the jet. However, there is still a need for substantial further improvement.
There have been some apparatus and methods developed for controlling and enhancing the distribution of moving streams of air, in addition to the planar jet and air entrainment process described above. For example, U.S. Pat. No. 3,242,846 issued to Bunn and U.S. Pat. No. 4,823,681 issued to Gore utilize rotating disks located in or near the nozzle outlet of a fresh air ducts to continuously deflect the flow direction of the jets. The Hinden patent, U.S. Pat. No. 2,972,358 discloses a fixed mechanical apparatus for directing the flow of air through ducts. U.S. Pat. No. 681,215 issued to Goll discloses an apparatus for equalizing air flow in rooms or ducts caused by unequal pressure drops. Air is forced through conduits of somewhat equal path lengths resulting in equal pressure drops and more uniform flow distribution. The Ferris patent, U.S. Pat. No. 2,212,468 discloses an adjustable disk that both deflects air and controls the flow rate by constricting the diffuser opening.
The above patents address the issue of poor air distribution by physically deflecting the air to continuously changing directions. A disadvantage of merely deflecting the air is that the fluid structure of the jet (other than being redirected), remains unaffected, thus the mixing and entrainment of the jet remains substantially unchanged. If entrainment could be increased, mixing would be enhanced and should lead to better room air distribution, enhanced dilution and removal of contaminants, and sufficiently low jet velocities to ensure occupant comfort.